Improving radar rainfall estimates at Kwajalein Atoll, RMI through relative calibration adjustments

The TRMM Satellite Validation Office (TSVO) at the Goddard Space Flight Center (GSFC) has developed a technique to quantify and apply Relative Calibration Adjustments (RCA) to reflectivity data from the Kwajalein Atoll S-band radar (KPOL) for the TRMM Ground Validation (GV) program. The technique is based on the analysis of radar ground clutter pixels, and results in daily reflectivity calibration adjustments. Improvements to KPOL rainfall estimates from application of the RCA have been quantified, and comparisons with the TRMM satellite rain rate algorithms have been performed. Compared with previous rainfall estimates (Version 5, TRMM GV products), radar rainfall with applied RCA converges with rain rate estimates from both rain gauge and TRMM satellite algorithms. In years with known and significant calibration issues (e.g. 2000 and 2003), radar rainfall estimation decreased by 30-50% after application of the RCA. Independent comparisons of these ground-based rain rate estimates with Version 6 TRMM PR (2A-25), TMI (2A-12), and COMBINED (2B-31) algorithms show significant bias decreases from prior GV estimates, thereby revealing the importance of calibration stability in radar rainfall estimation.